Particles for electrophoretic displays

ABSTRACT

This invention relates to particles comprising a pigment core particle encapsulated by a polymer, a process for their preparation, electrophoretic fluids comprising such particles, and electrophoretic display devices comprising such fluids.

This invention relates to particles comprising a pigment core particleencapsulated by a polymer, a process for their preparation,electrophoretic fluids comprising such particles, electrophoreticdisplay devices comprising such fluids, and the use of the particles inoptical, electrooptical, electronic, electrochemical,electrophotographic, electrowetting and electrophoretic displays and/ordevices, in security, cosmetic, decorative or diagnostic applications.

EPDs (Electrophoretic Displays) and their use for electronic paper havebeen known for a number of years. An EPD generally comprises chargedelectrophoretic particles dispersed between two substrates, eachcomprising one or more electrodes. The space between the electrodes isfilled with a dispersion medium which is a different colour from thecolour of the particles. If a voltage is applied between the electrodes,charged particles move to the electrode of opposite polarity. Theparticles can cover the observer's side electrode, so that a colouridentical to the colour of the particles is displayed when an image isobserved from the observer's side. Any image can be observed using amultiplicity of pixels. Mainly black and white particles are used.

Particles suitable for use in electrophoretic displays (EPD), e.g.coloured electronic paper have been exemplified in recent patentliterature; e.g. (U.S. Pat. No. 7,304,634, GB 2 438 436, US2007/0268244, WO 2010/089057, WO 2012/019704). Particles coated with asurface layer to promote good dispersibility in dielectric media aredisclosed in WO 2004/067593, US 2011/0079756, U.S. Pat. No. 5,964,935,U.S. Pat. No. 5,932,633, U.S. Pat. No. 6,117,368, WO 2010/148061, WO2002/093246, WO 2005/036129, US 2009/0201569, U.S. Pat. No. 7,236,290,JP 2009031329, U.S. Pat. No. 7,880,955, and JP 2008122468. The use ofpolydimethylsiloxane stabilisers in the specific synthesis of polymerparticles is described in the state of the art (Kim et al, MaterialsScience and Engineering, C 27 (2007), 1247-1251; Klein et al, ColloidPolym Sci (2003) 282: 7-13; JP 2009256635, JP 2008274248, JP2008274249).

However, there continues to be a need for improved electrophoreticfluids and coloured polymer particles which can be easily prepared anddispersed in non-polar media.

The present invention relates to particles comprising pigment coreparticles encapsulated by a polymer comprising monomer units of at leastone polymerisable dye, at least one polymerisable steric stabiliser, atleast one co-monomer, optionally at least one charged co-monomer, andoptionally at least one crosslinking co-monomer, a process for theirpreparation, the use of the particles in electrophoretic fluids, andelectrophoretic display devices comprising these fluids. The subjectmatter of this invention specifically relates to reflective colouredparticles, and to electrophoretic fluids and displays comprising suchreflective coloured particles.

Preferably, the present invention relates to particles comprising asingle pigment core particle encapsulated by a polymer as describedabove and wherein the particles comprise at least one surfactant.

In particular, the present invention relates to particles comprising asingle pigment core particle coated with at least one surfactant andencapsulated by a polymer as described above. Such particles have thefurther advantage that the pigment core particle, i.e. titanic (titaniumdioxide) is located near the centre of particles and is well dispersed.

The present coloured particles are hybrid polymer/pigment particles.These particles can comprise a highly reflective pigment core,especially titania core, combined with a dye. This has the effect ofincreasing the reflectivity or ‘Y’ value of the coloured particle. The Yvalue is derived from the CIE colour space system, where Y is defined tobe the brightness or luminance. The particles do not show a detrimentaleffect on hue, i.e. if a particle is prepared by combining TiO₂ with amagenta dye and forms a particle, the shade of magenta does not shift toyellow or blue, it simply appears a brighter magenta as it shiftstowards the white point.

Furthermore, if reduction of settling is a more important factor, theparticles may comprise white SiO₂ particles which have a low density. Acombination of core particles may also be used.

The invention provides a method to produce particles suitable for use inEPD which have controllable size, reflectivity, density, monodispersity,and steric stability and require no drying process to disperse in asolvent suitable for EPD. Advantageously, the invention providescoloured particles with increased reflectivity. So, EPD displayscomprising reflective coloured particles of the invention appear brightand appealing to a viewer.

The present invention provides particles, especially reflective colouredparticles which can be easily dispersed in nonpolar media and showelectrophoretic mobility. Particle size, polydispersity, and density canbe controlled and the present incorporation of pigment into polymericparticles does neither require multiple process steps nor expensivedrying steps, i.e. freeze drying. The present process involves onesimple polymerisation step. The present process facilitates theformulation of electrophoretic fluids since it is done in a non-polarorganic solvent instead of aqueous media. The particles can be preparedin the solvent of choice for EPD formulations, therefore no unwantedsolvent contamination occurs and no disposal or recycling of solvent isnecessary. Particles of the invention are easily dispersed indielectric, organic media, which enables switching of the particles inan applied electric field, preferably as the electrically switchablecomponent of a full colour e-paper or electrophoretic display.

The present coloured polymer particles can be produced by encapsulatingat least one highly reflective inorganic or organic pigment particle inan organic coloured polymer by a dispersion polymerisation. This yieldsa coloured hybrid particle which exhibits excellent reflectivity wherethe inorganic material is encapsulated by a tough polymer that forms apolymeric shell. This tough shell prevents particle agglomeration.

Advantageously, surfactants can be used to separate pigment particleswhile still allowing them to be encapsulated by the polymer. Inparticles not comprising a surfactant pigment particles may beaggregated and this may result in lower reflectivity. By control oflevel of surfactant, the pigment particles are dispersed well in thepolymer particles.

Particles of the invention comprise sterical stabilisers covalentlybonded into the pigment core particles. Advantageously, the presentinvention does not require custom synthesised stabilisers with difficultto control steric lengths and multistep complex syntheses with expensiveor difficult to synthesise components.

The invention enables the synthesis of new coloured, preferablycross-linked polymer particles for EPD and allows formation ofmonodisperse polymer particles in a non-polar solvent suitable for usein an EPD. No solvent transfer or drying is required. A stericstabiliser is readily incorporated into the coloured polymer particleswhich do not need specific chemical groups and/or reactions. Thestabiliser solely needs the presence of another monomer and ispolymerised into the particle and cannot be removed by solvent washingor over time. The particles may comprise at least 5% by weight of asteric stabiliser, preferably at least 20% by weight, based on theweight of the polymer particles. Dyes are also irreversibly entangledinto the forming polymer particles as well as the stabiliser, so thatthe dye is not able to leach from the particle over a long time period.Advantageously, the coloured polymeric particles of the invention have amuch lower density than inorganic pigment particles whose use has beenreported in EPD. In an EPD, these particles should settle much moreslowly than inorganic pigment particles, allowing for betterbistability. Additionally, the particles do not swell in non-polar EPDsolvents especially when cross-linked through dyes with more than onepolymerisable group and/or additional cross-linking co-monomers.Furthermore, the coloured polymer particles of the invention, preferablycyan, magenta and yellow particles have good mobility when switched inan electrophoretic cell.

An essential component of the present invention is a polymerisable dyecomprising at least one polymerisable group, preferably at least twopolymerisable groups. By use of a dye with 2 or more polymerisablegroups, the dye does not leach into the solvent. In general thepolymerisable dyes may be solvent soluble or water soluble and they maybe anionic, cationic, zwitterionic or neutral. Preferably, an ionic,water soluble dye could be used which is also insoluble in dodecane.

Cationic polymerisable dyes contain a covalently attached group orgroups which have a positive charge in the application or contain apositive charge in the chromophore group. They can be derived fromprotonation or quaternation of nitrogen, phosphorous, oxygen or sulphuratoms or groups containing them, for example heteroaromatic (thiazole,imidazole) delocalised nitrogen bases (guanidine etc). Associated anionspreferably have a single charge and can preferably be halogen,preferably F⁻, Cl⁻, Br⁻, monobasic acid (oxo) anions, preferablyacetate, propionate, lactate, methane sulphonate, p-toluenesulphonate,hydroxide, and nitrate.

Preferred examples of water soluble cationic polymerisable dyes compriseas counter ion MeOSO₃ ⁻. Also preferably suitable are Cl⁻, Br⁻, andacetate.

Anionic polymerisable dyes contain a covalently attached group or groupswhich have a negative charge in the application and can be derived fromdeprotonation of an acidic group for example sulphonic, carboxylic,phosphonic acids. Associated cations preferably have a single charge andcan be metallic (Li⁺, Na⁺, K⁺ etc), charged nitrogen (NH₄ ⁺, NEt₃H⁺,NEt₄ ⁺, NMe₄ ⁺, imidazolium cation etc), positively charged phosphorous,sulphur etc. Preferred examples of water soluble anionic dyes are theNa⁺, NH₄ ⁺, NEt₄ ⁺ salts of the acids.

The function of the polymerisable dye is to colour the particle. Thepolymerisable dye consists of a chromophore, at least two polymerisablegroups, optional linker groups (spacers), and optional groups to modifyphysical properties (like solubility, light fastness, etc.) andoptionally charged group(s).

The polymerisable dye preferably comprises a chromophoric group and twopolymerisable groups selected from e.g. methacrylates, acrylates,methacrylamides, acrylamides, acrylonitriles, α-substituted acrylates,styrenes and vinyl ethers, vinyl esters, propenyl ethers, oxetanes andepoxys etc., in particular methacrylates and acrylates.

A polymerisable dye may contain a single chromophore, for example withbright yellow, magenta or cyan colours and self shade blacks. However,it may also contain mixed covalently attached chromophores for exampleto obtain a black colour, by covalently attached brown and blue oryellow, magenta and cyan. Green can be obtained by yellow and cyan etc.Extended conjugated chromophores can also be used to obtain some shades.For example, bis- and trisazo compounds can be used to obtain blacks andother duller shades (navy blue, brown, olive green, etc).

Mixtures of polymerisable dyes can also be used to obtain the correctparticle shade; for example a black from single component mixtures ofbrown and blue or yellow, magenta and cyan pre-polymerised dyes.Similarly shades can be tuned for example by adding small quantities ofseparate polymerisable dyes to modify the colour of the particles (e.g.95% yellow and 5% cyan to get a greener yellow shade).

Modified polymerisable dyes (with reactive group(s)) from theapplication groups of reactive (anionic), direct (anionic), acidic(anionic) and basic (cationic) dyes as designated by the Colour Index(published by The Society of Dyers and Colourists with the AmericanAssociation of Textile Chemists and Colorists e.g. 3^(rd) edition 1982)are preferred.

The polymerisable groups may be attached directly to the chromophoricgroup or may be attached through a linker group L.

The chromophoric group preferably comprises of conjugated aromatic(including heteroaromatic) and/or multiple bonds including: azo(including monoazo, bisazo, trisazo, linked azos etc), metallised azo,anthraquinone, pyrroline, phthalocyanine, polymethine, aryl-carbonium,triphendioxazine, diarylmethane, triarylmethane, anthraquinone,phthalocyanine, methine, polymethine, indoaniline, indophenol, stilbene,squarilium, aminoketone, xanthene, fluorone, acridene, quinolene,thiazole, azine, induline, nigrosine, oxazine, thiazine, indigoid,quinonioid, quinacridone, lactone, benzodifuranone, flavonol, chalone,polyene, chroman, nitro, naphtholactam, formazene or indolene group or acombination of two or more such groups.

Preferred polymerisable dyes are azo dyes, metallised dyes,anthraquinone dyes, phthalocyanine dyes, benzodifuranones dyes,Brilliant Blue derivatives, pyrroline dyes, squarilium dyes,triphendioxazine dyes or mixtures of these dyes, especially azo dyes,metallised dyes, anthraquinone dyes, phthalocyanine dyes,benzodifuranones dyes, pyrroline dyes, squarilium dyes or mixtures ofthese dyes.

Preferably dyes with more than one polymerisable group are used. Inprinciple any polymerisable dye can be used, preferable with more thanone polymerisable group (most preferably with 2 polymerisable groups)and preferably with a methacrylate or acrylate function. Advantageously,the polymerisable dyes disclosed in WO2010/089057 and WO2012/019704 areused. Preferably dyes of Formulas (I′)-(VI′) are used:

wherein R is H; R1 and R2 are independently of one another alkyl,preferably C1-C6 alkyl, —OR′, —SR′, —C(O)R′, —C(O)OR′, —NHCOR′, —NO₂,—CN, with R′ equal to H or alkyl, preferably C1-C6 alkyl, especiallyC1-C3 alkyl; L¹ and L² are independently of one another a single bond,C1-C6 alkyl, a polyether alkyl chain, or a combination thereof,preferably C2-C4 alkyl, especially C2 and C4 alkyl, especially identicalgroups L¹ and L² are preferred; and Y¹ and Y² are methyl acrylate ormethyl methacrylate, especially identical groups Y¹ and Y² arepreferred.

Especially preferred are polymerisable dyes of Formulas (I′)-(VI′)wherein R is H; R1 and R2 are independently of one another —CH₃, —NO₂,—OH, —CN, —COCH₃, —CO₂CH₂CH₃, —NHCOR′; L¹ and L² are, preferablyidentical, C2-C4 alkyl, and Y¹ and Y² are, preferably identical, methylacrylate or methyl methacrylate, wherein R2 is preferably —CH₃, —OH or—NHCOR′.

Also polymerisable dyes of Formula (VII) are preferably used.

Wherein

X₁, X₂, and X₃ are independently of one another H or anelectron-withdrawing group;R₁ is H or OR′ with R′=a linear, branched or cyclic alkyl group;R₂ is a linear, branched or cyclic alkyl group;R₃ and R₄ are independently of one another groups of the structureL₃-Y₃, L₄-Y₄.L₃, and L₄ are linker groups and independently of one another linear orbranched, substituted or unsubstituted alkylene groups where one or morenon-adjacent carbon atoms may be replaced by O, S and/or N, preferablyO;Y₃, and Y₄ are independently of one another polymerisable groups;

Wherein at least one of R₃ and R₄ comprises a polymerisable group and atleast one of X₁, X₂, and X₃ is an electron-withdrawing group.

The term “electron-withdrawing group” is well known in the art andrefers to the tendency of a substituent to attract valence electronsfrom neighbouring atoms; in other words the substituent iselectronegative with respect to neighbouring atoms. Examples ofelectron-withdrawing groups include NO₂, CN, halogen, acyl,trifluoromethoxy, trifluoromethyl, SO₂F, and CO₂R, SO₂R, SO₂NRR orSO₂NHR, with R being independently linear or branched alkyl, preferablyC1-C4 alkyl. Preferably, at least one of X₁, X₂, and X₃ is NO₂, CN, Br,Cl, SO₂NRR or SO₂NHR. Especially preferred are polymerisable dyes withX₂ and one of X₁ and X₃ being NO₂, CN, Br, Cl, SO₂NRR or SO₂NHR,preferably with R=methyl. Also preferred are polymerisable dyes with X₂being NO₂, CN, Br, Cl, SO₂NRR or SO₂NHR, preferably with R=methyl, andX₁ and X₃ being H.

The polymerisable groups Y₃, and Y₄ may be selected from e.g.methacrylate, acrylate, methacrylamide, acrylamide, oxetanes, vinyl,vinyloxy, epoxy, allyl, propenyl ether, styryl groups, in particularmethacrylate, acrylate, methacrylamide, and acrylamide. Preferably,groups Y₃, and Y₄ are selected from methacrylate and acrylate.

R₁ and R₂ are preferably C1-C20 alkyl groups, especially alkyl groupshaving 1 to 10 carbon atoms. C2-C8 alkyl groups are even more preferred.

R₃ and R₄ are independently of one another groups of the structure L₃-Y₃or L₄-Y₄, preferably L₃ and L₄ are independently of one another linearor branched C1-C20 alkylene groups, especially alkylene groups having 1to 10 carbon atoms. Linear C2-C6 alkylene groups are even morepreferred. Especially groups where Y₃ and Y₄ are methacrylate oracrylate are preferred. Especially identical groups Y₃ and Y₄ arepreferred.

Preferred polymerisable dyes are in particular those dyes in which allvariables have the preferred meanings.

The following are examples of dyes which can preferably be used:

TABLE 1 Dye 1 

Dye 2 

Dye 3 

Dye 4 

Dye 5 

Dye 6 

Dye 7 

Dye 8 

Dye 9 

Dye 10

Dye 11

Dye 12

Dye 13

Dye 14

Dye 15

Dye 16

Dye 17

Dye 18

Most preferred are the following dyes: Dye 1, Dye 2, Dye 3, and Dye 4.

Polymerisable dyes, especially the preferred polymerisable dyes can beprepared according to the processes described in WO2010/089057 andWO2012/019704, especially according to WO2012/019704.

The preparation of polymerisable dyes of Formula (VII) by a 7 stepprocedure under convenient conditions as known in the art is exemplifiedin the following scheme for(E)-4,4′-(4-((2,6-dicyano-4-nitrophenyl)diazenyl)-2-methoxy-5-(3,5,5-trimethylhexanamido)phenylazanediyl)bis(butane-4,1-diyl)diacrylate(Dye 3):

Primarily, the invention provides reflective coloured particles byincorporating an inorganic material of sufficiently high refractiveindex and white reflectivity into a coloured organic polymer basedparticle to yield a hybrid polymeric particle which exhibits goodreflective properties. Preferably, white reflective particles are usedhaving a refractive index of ≧1.8, especially ≧2.0, are used. Especiallytitanium dioxide (titania), zinc oxide, silicon dioxide, alumina, bariumsulphate, zirconium dioxide, calcium carbonate, kaolinite, diantimonytrioxide and/or tin dioxide, especially titanium dioxide, can be used.

Preferably, titanium dioxide based pigments are used which could havethe rutile, anatase, or amorphous modification, preferably rutile oranatase, Examples are: Sachtleben RDI-S, Sachtleben R610-L, SachtlebenLC-S, Kronos 2081, Kronos 2305, Sachtleben Hombitan Anatase, SachtlebenHombitan Rutile, Du Pont R960, Du Pont R350, Du Pont R104, Du Pont R105,Du Pont R794, Du Pont R900, Du Pont R931, Du Pont R706, Du Pont R902+,Du Pont R103, Huntsman TR-81, Huntsman TR-28, Huntsman TR-92, HuntsmanR-TC30, Huntsman R-FC5, Evonik P25, Evonik T805, Merck Eusolex T2000,Merck UV Titan M765. Preferably, Du Pont R960, and Sachtleben HombitanAnatase are used.

The invention allows density control by tunability of the shell aroundthe inorganic core pigment. The amount of the organic polymeric materialin the reaction can be increased relative to the inorganic pigment whichresults in a lower density particle, or if higher density is desired,the pigment ratio can be increased.

Pigments encapsulated within the particles are preferably well dispersedin a non-aggregated state in order to achieve the optimum opticalproperties. If the pigment is high density, the optimum loading of thepigment within polymer may not only be affected by the opticalproperties but also the density of the resulting particle in order toachieve improved bistability. Pigments are present in the particle (onweight of total particle) from 5-95%, preferably 20-80% and even morepreferably 30-60%.

A further essential component of the present invention is apolymerisable steric stabiliser. The polymerisable steric stabilisersneed to be soluble in non-polar solvents, particularly dodecane, andhave some reactive functionality such that they take part in thepolymerisation. This creates a particle with a covalently bound surfaceof sterically stabilising compounds providing stability during and afterpolymerisation. The polymerisable steric stabiliser can be used in arange of molecular weights which allows strict control over the stericbarrier surrounding the particles to prevent aggregation. Thepolymerisable group incorporates irreversibly into the particles and istherefore anchored to the surface.

A typical polymerisable steric stabiliser of the invention is apoly(dimethylsiloxane) macro-monomer (PDMS). The poly(dimethylsiloxane)may comprise one or two polymerisable groups, preferably onepolymerisable group.

The following stabiliser types could be used and are commerciallyavailable from Gelest Inc.:

Methacryloyloxypropyl terminated polydimethylsiloxanes (mws 380, 900,4500, 10000, 25000) Methacryloyloxypropyl terminatedpolydimethylsiloxanes (mw 600), Methacryloyloxypropyl terminatedpolydimethylsiloxanes (1500, 1700), (3-acryloxy-2-hydroxypropoxypropyl)terminated PDMS (mw 600), Acryloxy terminatedethyleneoxide-dimethylsiloxane-ethyleneoxide ABA block copolymers (mw1500, 1700), methacyloyloxpropyl terminated branchedpolydimethylsiloxanes (683),(methacryloxypropyl)methylsiloxanes-Dimethylsiloxane copolymers(viscosity 8000, 1000, 2000),(acryloxypropyl)methylsiloxane-dimethylsiloxanes copolymers (viscosity80, 50),(3-acryloxy-2-hydroxypropoxypropyl)methylsiloxane-dimethylsiloxanecopolymers (mw 7500), mono(2,3-epoxy)propyl ether terminatedpolydimethylsilxoanes (mw 1000, 5000), monomethacryloxypropyl terminatedpolydimethylsiloxanes asymmetric (mw 600, 800, 5000, 10000),monomethacryloxypropyl functional polydimethylsiloxanes-symmetric (mw800), monomethacryloxypropyl terminatedpolytrifluoropropylmethylsiloxanes-symmetric (mw 800) monovinylterminated polydimethylsiloxanes (mw 5500, 55000, monovinyl functionalpolydimethylsilxanes-symmetric (mw 1200).

Preferred polymerisable groups are methacrylate, acrylate, and vinylgroups, preferably methacrylate and acrylate groups. Most preferred arepoly(dimethylsiloxane) methacrylates (PDMS-MA), especiallymethacryloyloxypropyl terminated PDMS-MAs as shown in Formulas 1 and 2,wherein n=5-10000. Most preferred are poly(dimethylsiloxanes) with onemethacrylate group.

The polymerisable steric stabiliser of the invention preferably has amolecular weight in the range of 1000-50000, preferably 3500-35000, mostpreferably 5000-25000. Most preferred are methacrylate terminatedpolydimethylsiloxanes with a molecular weight of 10,000 or more,especially 10000-25000.

Preferably, at least one surfactant is used as additional component forparticles of the present invention. Typical surfactants are soluble inaliphatic solvents used for polymerisation and have an oil soluble tailto provide stability with a hydrophilic head to provide adsorption tothe pigment particle surface. Typical surfactants used in this processare cationic, anionic, zwitterionic or non-ionic with a hydrophilicportion usually termed the head group which is mono-, di- orpolysubstituted with a hydrophobic portion usually termed the tail. Thehydrophilic head group of the surfactant in this process can be, but isnot limited to being, made up of derivatives of sulfonates, sulfates,carboxylates, phosphates, ammoniums, quaternary ammoniums, betaines,sulfobetaines, imides, anhydrides, polyoxyethylene (eg. PEO/PEG/PPG),polyols (eg. sucrose, sorbitan, glycerol etc), polypeptides andpolyglycidyls. The hydrophobic tail of the surfactant in this processcan be, but is not limited to being, made up of straight and branchedchain alkyls, olefins and polyolefins, rosin derivatives, PPO, hydroxyland polyhydroxystearic acid type chains, perfluoroalkyls, aryls andmixed alkyl-aryls, silicones, lignin derivatives, and partiallyunsaturated versions of those mentioned above. Surfactants for thisprocess can also be catanionic, bolaforms, gemini, polymeric andpolymerisable type surfactants. Preferably, polyisobutylene succinimidesmay be used.

Examples of preferred surfactants are the Span, Brij and Tween range(Sigma-Aldrich), the Solsperse, Ircosperse and Colorburst range(Lubrizol), the OLOA range (Chevron Chemicals) and Aerosol-OT (A-OT)(Aldrich), A-OT (dioctyl sulfosuccinate sodium salt), Span 80 and Span85 (partially unsaturated sorbitan trioleate), Solsperse 17000, and OLOA1100 are particularly useful to disperse and coat titania in thisreaction. Single surfactants as well as blends of surfactants may beused.

The particles of the invention can be prepared from many polymer types.Preferably, monomers are used where the monomer is soluble in thereactive mixture and the polymer is insoluble in the reactive mixturewith relatively high Tg. This allows hard composite particles to beformed which tend to be spherical in shape and have easily tunable size.

The main requirement for the polymer composition is that it needs to beproduced from a monomer that is soluble but polymer insoluble in the EPDfluid, i.e. dodecane and can also provide some linkage to the surface ofthe titania during polymerisation. Low solubility of the polymermaterial in the EPD dispersion media reduces the tendency for ripeningprocesses to take place and helps define the particle size and sizedispersity.

The particles can be prepared from most monomer types, in particularmethacrylates, acrylates, methacrylamides, acrylonitriles, α-substitutedacrylates, styrenes and vinyl ethers, vinyl esters, propenyl ethers,oxetanes and epoxys but would typically be prepared from largestpercentage to be monomer, then cross-linker, and include a chargedmonomer (e.g. quaternised monomer). Especially preferred is methylmethacrylate but many others could be used, the following are allexamples of which could be used which are commercially available fromthe Sigma-Aldrich chemical company. Mixtures of monomers may also beused.

Methacrylates:

Methyl methacrylate (MMA), Ethyl methacrylate (EMA), n-Butylmethacrylate (BMA), 2-Aminoethyl methacrylate hydrochloride, Allylmethacrylate, Benzyl methacrylate, 2-Butoxyethyl methacrylate,2-(tert-Butylamino)ethyl methacrylate, Butyl methacrylate, tert-Butylmethacrylate, Caprolactone 2-(methacryloyloxy)ethyl ester,3-Chloro-2-hydroxypropyl methacrylate, Cyclohexyl methacrylate,2-(Diethylamino)ethyl methacrylate, Di(ethylene glycol) methyl ethermethacrylate, 2-(Dimethylamino)ethyl methacrylate, 2-Ethoxyethylmethacrylate, Ethylene glycol dicyclopentenyl ether methacrylate,Ethylene glycol methyl ether methacrylate, Ethylene glycol phenyl ethermethacrylate, 2-Ethylhexyl methacrylate, Furfuryl methacrylate, Glycidylmethacrylate, Glycosyloxyethyl methacrylate, Hexyl methacrylate,Hydroxybutyl methacrylate, 2-Hydroxyethyl methacrylate, 2-Hydroxyethylmethacrylate, Hydroxypropyl methacrylate Mixture of hydroxypropyl andhydroxyisopropyl methacrylates, 2-Hydroxypropyl 2-(methacryloyloxy)ethylphthalate, Isobornyl methacrylate, Isobutyl methacrylate,2-Isocyanatoethyl methacrylate, Isodecyl methacrylate, Laurylmethacrylate, Methacryloyl chloride, Methacrylic acid,2-(Methylthio)ethyl methacrylate, mono-2-(Methacryloyloxy)ethyl maleate,mono-2-(Methacryloyloxy)ethyl succinate, Pentabromophenyl methacrylate,Phenyl methacrylate, Phosphoric acid 2-hydroxyethyl methacrylate ester,Stearyl methacrylate, 3-Sulfopropyl methacrylate potassium salt,Tetrahydrofurfuryl methacrylate, 3-(Trichlorosilyl)propyl methacrylate,Tridecyl methacrylate, 3-(Trimethoxysilyl)propyl methacrylate,3,3,5-Trimethylcyclohexyl methacrylate, Trimethylsilyl methacrylate,Vinyl methacrylate.

Preferably Methyl methacrylate (MMA), Methacrylic acid, Ethylmethacrylate (EMA), and/or n-Butyl methacrylate (BMA) are used.

Acrylates:

Acrylic acid, 4-Acryloylmorpholine,[2-(Acryloyloxy)ethyl]trimethylammonium chloride,2-(4-Benzoyl-3-hydroxyphenoxy)ethyl acrylate, Benzyl 2-propylacrylate,2-Butoxyethyl acrylate, Butyl acrylate, tert-Butyl acrylate,2-[(Butylamino)carbonyl]oxy]ethyl acrylate, tert-Butyl 2-bromoacrylate,4-tert-Butylcyclohexyl acrylate, 2-Carboxyethyl acrylate, 2-Carboxyethylacrylate oligomers anhydrous, 2-(Diethylamino)ethyl acrylate, i(ethyleneglycol) ethyl ether acrylate technical grade, Di(ethylene glycol)2-ethylhexyl ether acrylate, 2-(Dimethylamino)ethyl acrylate,3-(Dimethylamino)propyl acrylate, Dipentaerythritolpenta-/hexa-acrylate, 2-Ethoxyethyl acrylate, Ethyl acrylate,2-Ethylacryloyl chloride, Ethyl 2-(bromomethyl)acrylate, Ethylcis-(β-cyano)acrylate, Ethylene glycol dicyclopentenyl ether acrylate,Ethylene glycol methyl ether acrylate, Ethylene glycol phenyl etheracrylate, Ethyl 2-ethylacrylate, 2-Ethylhexyl acrylate, Ethyl2-propylacrylate, Ethyl 2-(trimethylsilylmethyl)acrylate, Hexylacrylate, 4-Hydroxybutyl acrylate, 2-Hydroxyethyl acrylate,2-Hydroxy-3-phenoxypropyl acrylate, Hydroxypropyl acrylate, Isobornylacrylate, Isobutyl acrylate, Isodecyl acrylate, Isooctyl acrylate,Lauryl acrylate, Methyl 2-acetamidoacrylate, Methyl acrylate, Methylα-bromoacrylate, Methyl 2-(bromomethyl)acrylate, Methyl3-hydroxy-2-methylenebutyrate, Octadecyl acrylate, Pentabromobenzylacrylate, Pentabromophenyl acrylate, Poly(ethylene glycol) methyl etheracrylate, Poly(propylene glycol) acrylate, Poly(propylene glycol) methylether acrylate Soybean oil, epoxidised acrylate, 3-Sulfopropyl acrylatepotassium salt, Tetrahydrofurfuryl acrylate, 3-(Trimethoxysilyl)propylacrylate, 3,5,5-Trimethylhexyl acrylate.

Preferably Methyl acrylate, acrylic acid, Ethyl acrylate (EMA), and/orn-Butyl acrylate (BMA) are used.

Acrylamides:

2-Acrylamidoglycolic acid, 2-Acrylamido-2-methyl-1-propanesulfonic acid,2-Acrylamido-2-methyl-1-propanesulfonic acid sodium salt solution,(3-Acrylamidopropyl)trimethylammonium chloride solution,3-Acryloylamino-1-propanol solution purum, N-(Butoxymethyl)acrylamide,N-tert-Butylacrylamide, Diacetone acrylamide, N,N-Dimethylacrylamide,N-[3-(Dimethylamino)propyl]methacrylamide, N-Hydroxyethyl acrylamide,N-(Hydroxymethyl)acrylamide, N-(Isobutoxymethyl)acrylamide,N-Isopropylacrylamide, N-Isopropylmethacrylamide, Methacrylamide,N-Phenylacrylamide, N-[Tris(hydroxymethyl)methyl]acrylamide.

Styrenes

Styrene, Divinyl benzene, 4-Acetoxystyrene,4-Benzyloxy-3-methoxystyrene, 2-Bromostyrene, 3-Bromostyrene,4-Bromostyrene, α-Bromostyrene, 4-tert-Butoxystyrene,4-tert-Butylstyrene, 4-Chloro-α-methylstyrene, 2-Chlorostyrene,3-Chlorostyrene, 4-Chlorostyrene, 2,6-Dichlorostyrene,2,6-Difluorostyrene, 1,3-Diisopropenylbenzene, 3,4-Dimethoxystyrene,α,2-Dimethylstyrene, 2,4-Dimethylstyrene, 2,5-Dimethylstyrene,N,N-Dimethylvinylbenzylamine, 2,4-Diphenyl-4-methyl-1-pentene,4-Ethoxystyrene, 2-Fluorostyrene, 3-Fluorostyrene, 4-Fluorostyrene,2-Isopropenylaniline, 3-Isopropenyl-α,α-dimethylbenzyl isocyanate,Methylstyrene, α-Methylstyrene, 3-Methylstyrene, 4-Methylstyrene,3-Nitrostyrene, 2,3,4,5,6-Pentafluorostyrene,2-(Trifluoromethyl)styrene, 3-(Trifluoromethyl)styrene,4-(Trifluoromethyl)styrene, 2,4,6-Trimethylstyrene. Preferably Styreneand/or Divinyl benzene are used.

Vinyl Groups

3-Vinylaniline, 4-Vinylaniline, 4-Vinylanisole, 9-Vinylanthracene,3-Vinylbenzoic acid, 4-Vinylbenzoic acid, Vinylbenzyl chloride,4-Vinylbenzyl chloride, (Vinylbenzyl)trimethylammonium chloride,4-Vinylbiphenyl, 2-Vinylnaphthalene, 2-Vinylnaphthalene, Vinyl acetate,Vinyl benzoate, Vinyl 4-tert-butylbenzoate, Vinyl chloroformate, Vinylchloroformate, Vinyl cinnamate, Vinyl decanoate, Vinyl neodecanoate,Vinyl neononanoate, Vinyl pivalate, Vinyl propionate, Vinyl stearate,Vinyl trifluoroacetate.

Other monomers which may be used are those which have groups to helpstabilisation of the particles, e.g. Poly(ethylene glycol) methyl etheracrylate, Poly(ethylene glycol) phenyl ether acrylate, laurylmethacrylate, Poly(ethylene glycol) methyl ether acrylate,Poly(propylene glycol) methyl ether acrylate, Lauryl acrylate andfluorinated monomers of above.

Some of the monomers have groups for further reaction if so desired,e.g. Glycidyl ethacrylate, 2-Hydroxyethyl methacrylate.

The following compounds can be used as intraparticle crosslinkingmonomers for solubility control and solvent swelling resistance:ethylene glycol dimethacrylate (EGDMA), allyl methacrylate (ALMA),divinyl benzene, Bis[4-(vinyloxy)butyl]adipate,Bis[4-(vinyloxy)butyl]1,6-hexanediylbiscarbamate,Bis[4-(vinyloxy)butyl]isophthalate,Bis[4-(vinyloxy)butyl](methylenedi-4,1-phenylene)biscarbamate,Bis[4-(vinyloxy)butyl]succinate, Bis[4-(vinyloxy)butyl]terephthalate,Bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate, 1,4-Butanediol divinylether, 1,4-Butanediol vinyl ether, Butyl vinyl ether, tert-Butyl vinylether, 2-Chloroethyl vinyl ether, 1,4-Cyclohexanedimethanol divinylether, 1,4-Cyclohexanedimethanol vinyl ether, Di(ethylene glycol)divinylether, Di(ethylene glycol) vinyl ether, Ethylene glycol butyl vinylether, Ethylene glycol vinyl ether, Tris[4-(vinyloxy)butyl]trimellitate,3-(Acryloyloxy)-2-hydroxypropyl methacrylate,Bis[2-(methacryloyloxy)ethyl]phosphate, Bisphenol A propoxylatediacrylate, 1,3-Butanediol diacrylate, 1,4-Butanediol diacrylate,1,3-Butanediol dimethacrylate, 1,4-Butanediol dimethacrylate,N,N′-(1,2-Dihydroxyethylene)bisacrylamide,Di(trimethylolpropane)tetraacrylate, Diurethane dimethacrylate,N,N′-Ethylenebis(acrylamide), Glycerol 1,3-diglycerolate, Glyceroldimethacrylate, 1,6-Hexanediol diacrylate, 1,6-Hexanedioldimethacrylate,1,6-Hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)]bisacrylate,Hydroxypivalyl hydroxypivalate bis[6-(acryloyloxy)hexanoate], Neopentylglycol diacrylate, Pentaerythritol diacrylate, Pentaerythritoltetraacrylate, Pentaerythritol triacrylate, Poly(propyleneglycol)diacrylate, Poly(propylene glycol)dimethacrylate,1,3,5-Triacryloylhexahydro-1,3,5-triazine,Tricyclo[5.2.1.0]decanedimethanol diacrylate, Trimethylolpropanebenzoate diacrylate, Trimethylolpropane ethoxylate methyl etherdiacrylate, Trimethylolpropane ethoxylate triacrylate,Trimethylolpropane triacrylate, Trimethylolpropane trimethacrylate,Tris[2-(acryloyloxy)ethyl] isocyanurate, Tri(propyleneglycol)diacrylate.

Optionally, the monomer composition comprises at least one chargedco-monomer.

Examples of cationic monomers for particle stability and particle sizecontrol are 2-methacryloxy ethyl trimethyl ammonium chloride (MOTAC),acryloxy ethyl trimethyl ammonium chloride (AOTAC),[3-(Methacryloylamino)propyl]trimethylammonium chloride,[2-(Methacryloyloxy)ethyl]trimethylammonium methyl sulfate solution,tetraallyl ammonium chloride, diallyl dimethyl ammonium chloride,(Vinylbenzyl)trimethylammonium chloride.

Preferably 2-methacryloxy ethyl trimethyl ammonium chloride (MOTAC) andacryloxy ethyl trimethyl ammonium chloride (AOTAC) are used.

Examples of anionic monomers are sodium, potassium or triethylaminesalts of methacrylic acid, Acrylic acid, 2-(Trifluoromethyl)acrylicacid, 3-(2-Furyl)acrylic acid, 3-(2-Thienyl)acrylic acid,3-(Phenylthio)acrylic acid, Poly(acrylic acid) potassium salt,Poly(acrylic acid) sodium salt, Poly(acrylic acid), Poly(acrylic acid,sodium salt) solution, trans-3-(4-Methoxybenzoyl)acrylic acid,2-Methoxycinnamic acid, 3-Indoleacrylic acid, 3-Methoxycinnamic acid,4-Imidazoleacrylic acid, 4-Methoxycinnamic acid,Poly(styrene)-block-poly(acrylic acid),Poly(acrylonitrile-co-butadiene-co-acrylic acid), dicarboxy terminated,Poly(acrylonitrile-co-butadiene-co-acrylic acid), dicarboxy terminated,glycidyl methacrylate diester,

2,3-Diphenyl-Acrylic Acid, 2-Me-Acrylic Acid, 3-(1-Naphthyl)AcrylicAcid, 3-(2,3,5,6-Tetramethylbenzoyl)Acrylic Acid,3-(4-Methoxyphenyl)Acrylic Acid, 3-(4-Pyridyl)Acrylic Acid,3-p-Tolyl-Acrylic Acid, 5-Norbornene-2-Acrylic Acid,Trans-3-(2,5-Dimethylbenzoyl)Acrylic Acid,Trans-3-(4-Ethoxybenzoyl)Acrylic Acid, Trans-3-(4-Methoxybenzoyl)AcrylicAcid, 2,2′-(1,3-Phenylene)Bis(3-(2-aminophenyl)Acrylic Acid),2,2′-(1,3-Phenylene)Bis(3-(2-Aminophenyl)Acrylic Acid) hydrochloride,2,2′-(1,3-Phenylene)Bis(3-(2-Nitrophenyl)Acrylic Acid),2-[2(2′,4′-Difluoro[1,1′-Biphenyl]-4-Yl)-2-Oxoethyl]Acrylic Acid,2-(2-(2-Chloroanilino)-2-Oxoethyl)-3-(4-Methoxyphenyl)Acrylic Acid,2-(2-((2-Hydroxyethyl)Amino)-2-Oxoethyl)-3-(4-Methoxyphenyl)AcrylicAcid, 2-(2-(Cyclohexylamino)-2-Oxoethyl)-3-(4-Methoxyphenyl)AcrylicAcid.

Especially preferred co-monomers are methyl methacrylate, methylacrylate, and methacrylic acid, acrylic acid, ethane-1,2 diacrylate,butane-1,4 diacrylate, hexane-1,6-diacrylate. Furthermore, mixtures ofco-monomers described in the foregoing may be used. Preferredco-monomers mixtures comprise methyl methacrylate, methyl acrylate,methacrylic acid, acrylic acid, ethane-1,2 diacrylate, butane-1,4diacrylate, hexane-1,6-diacrylate, trimethyloipropane triacrylate,2-methacryloxy ethyl trimethyl ammonium chloride (MOTAC) and/or acryloxyethyl trimethyl ammonium chloride (AOTAC).

Advantageously, the particles of the invention comprise a combination ofthe above-mentioned preferred compounds of pigment, polymerisable stericstabiliser, polymerisable dye, co-monomer, and optionally cross-linkingco-monomer. Most preferred are combinations of titanium dioxide,methacrylate terminated polydimethylsiloxanes with a molecular weight of10,000 or more, polymerisable dyes of Table 1, and methyl methacrylate.Especially, combinations of titanium dioxide, at least one polymerisabledyes of Table 1, surfactant (especially A-OT, Span 80 or Span 85,Solsperse 17000, OLOA 11000), methacrylate terminatedpolydimethylsiloxanes with a molecular weight of 10,000 or more, andmethyl methacrylate are preferred. In particular, the particles consistof titanium dioxide, at least one polymerisable dyes of Table 1,surfactant (especially A-OT, Span 80 or Span 85, Solsperse 17000, OLOA11000), methacrylate terminated polydimethylsiloxanes with a molecularweight of 10,000 or more, and methyl methacrylate.

Charging the polymer can also be facilitated by using an initiator whichis charged leaving that charge residing as an end-group on the polymer.Such examples are 2,2′-azobis(2-methylpropionamidine)dihydrochloride(V-50) (Wako Chemicals), potassium peroxodisulfate (KPS), ammoniumperoxodisulfate (APS), sodium peroxodisulfate (SPS),2,2′-azobiscyanovaleric acid (ACVA) (Wako Chemicals),2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA044) (WakoChemicals).

Charging does not have to come from the initiator fragment so initiatorswhich can also be used are those such as 2,2′-azobis(isobutyronitrile)(AIBN) (Wako Chemicals), 2,2′-azobis(2-methylbutyronitrile) (Vazo 67)(Wako Chemicals) and benzoyl peroxide.

A further subject of the invention is a process for the preparation ofparticles comprising a pigment core particle encapsulated by a polymer,wherein the polymer preferably comprises monomer units of at least onepolymerisable dye, at least one co-monomer, at least one polymerisablesteric stabiliser, optionally at least one charged co-monomer, andoptionally at least one crosslinking co-monomer.

Furthermore, the invention relates to a process for the preparation ofparticles comprising a single organic or inorganic pigment core particleencapsulated by a polymer and wherein the particles comprise at leastone surfactant.

In particular, the invention relates to a process for the preparation ofparticles comprising a single organic or inorganic pigment core particlecoated with at least one surfactant and encapsulated by a polymer,wherein the polymer preferably comprises monomer units of at least onepolymerisable steric stabiliser, at least one co-monomer, and optionallyat least one charged co-monomer, and optionally at least onecrosslinking co-monomer.

The present process comprises the following steps:

a) dispersing at least one pigment particle in a solution of at leastone polymerisable steric stabiliser in a non-polar organic solvent,preferably an aliphatic hydrocarbon;b) adding at least one polymerisable dye, at least one co-monomer, atleast one initiator, and optionally at least one chain transfer agent;c) subjecting the dispersion of step b) to heating and optionalsonication/milling/high shear mixing or stirring for polymerisation,d) optionally washing by repeated centrifugation or filtration,preferably stirred filtration, and redispersion in fresh solvent, ande) optionally isolating the resulting coated particles.

Preferably, the process comprises using at least one surfactant in stepa). Surfactant addition must be carefully controlled and optimized. Ifsurfactant level is too low, pigment is present as aggregates and if thelevel is too high pigment will not be encapsulated. Each pigment andsurfactant system has a slightly different optimum, though in general alevel of 4-8% surfactant on weight of pigment is usually around theoptimum level. The level varies due to differences in effectiveness andefficiency of surfactants and surface modification and surface area ofpigment. This process provides pigment particles, especially titania,wherein a single pigment particle is embedded in a coloured polymericshell by addition of a surfactant to the particles beforepolymerisation.

Optionally, the polymerisable compositions of the invention comprise achain transfer agent, e.g. catalytic chain transfer reagents, alkyl andaryl thiols, alcohols and carboxylic acids, halogenated organics andselected inorganic salts. Examples of suitable chain transfer agents are2-propanol, adipic acid, thioglycolic acid, 2-mercaptoethanol, sodiumhypochlorite, carbon tetrachloride and heavy metal poryphyrins,particularly cobalt poryphyrins preferably octane thiol.

The polymerisable composition of the invention usually comprises0.1-15%, preferably 2.0-13%, by weight of at least one polymerisabledye, 0.1-80%, preferably 20-60% by weight of at least one organic orinorganic pigment, preferably 10-40%, by weight of at least onepolymerisable steric stabiliser, 50-95%, preferably 60-90%, by weight ofco-monomer, optionally 1-40%, preferably 1-10%, by weight ofcross-linking co-monomer, optionally 1-30%, preferably 1-10%, by weightof charged co-monomer, optionally 0-3%, by weight of chain transferagent, and 0.1-10%, preferably 0.1-7.5%, by weight of initiator, allpercentages are based on the total weight of the polymerisablecomposition (except solvent).

Advantageously, the polymerisable composition of the invention comprisesin a non-polar hydrocarbon solvent, especially dodecane, 2.0-13% byweight of at least one of the above-mentioned preferred polymerisabledyes, 20-60% by weight of at least one of the above-mentioned preferredpigment particles, 1-10% by weight of at least one of theabove-mentioned preferred surfactants, 10-40% by weight of at least oneof the above-mentioned preferred polymerisable steric stabilisers,60-90% by weight of least one of the above-mentioned preferredpolymerisable co-monomers, 0.1-7.5% by weight of initiator, optionally1-10% by weight of cross-linking co-monomer, optionally 1-10% by weightof charged co-monomer, and optionally 0-3%, by weight of chain transferagent, wherein most preferably of titanium dioxide in the rutile oranatase modification, sorbitan mono or polyoleates as surfactant, atleast one of the dyes of Table 1, methacrylate terminatedpolydimethylsiloxanes with a molecular weight of 10,000 or more, andmethyl methacrylate are used.

The coloured polymer particles of the invention are preferably preparedusing a dispersion polymerisation. This is a convenient single stepmethod of preparing monodisperse coloured particles. It is performed ina fluid which is a good solvent for the monomer and a non-solvent forthe synthesised polymer particles. This solvent can also be used as thesame solvent for EPD, e.g. dodecane. The preferred solvents arenon-polar hydrocarbon solvents, especially such used in EPD fluids, i.e.the Isopar series (Exxon-Mobil), Norpar, Shell-Sol (Shell), Sol-Trol(Shell), naphtha, and other petroleum solvents, as well as long chainalkanes such as dodecane, tetradecane, decane and nonane. Especiallypreferred is dodecane. The concentration of the particles in thenon-polar solvent can be increased if desired by centrifugation, i.e.forced settling of the particles and pouring off excess solvent, or astirred cell filtration system can be used. The dispersion can be washedwith a non-polar solvent if required. If necessary, the coloured polymerparticles are simply separated from the reaction suspension byfiltration, preferably by pouring the suspension through a pore sizefilter, i.e. a 0.1 μm pore size filter, or the particles can be cleanedby centrifuging.

The selection of the polymerisation conditions depends on the requiredsize and size distribution of the particles. Adjustment ofpolymerisation conditions is well known to someone skilled in the art.

Preferably, a batch polymerisation process is used wherein all reactantsare completely added at the outset of the polymerisation process. Insuch process only relatively few variables have to be adjusted for agiven formulation. Preferred changes which can be made in such cases areto the reaction temperature, reactor design and the type and speed ofstirring.

Thus, a batch polymerisation process is used for manufacture versus asemi-continuous batch process because of limited versatility and simpleevaluations of reaction formulation.

Polymerisable compositions of the invention may additionally comprise asurfactant. Typical surfactants are soluble in aliphatic solvents usedfor polymerisation and have an oil soluble tail to provide stabilitywith a hydrophilic head to provide adsorption to the pigment particlesurface. Typical surfactants used in this process are cationic, anionic,zwitterionic or non-ionic with a hydrophilic portion usually termed thehead group which is mono-, di- or polysubstituted with a hydrophobicportion usually termed the tail. The hydrophilic head group of thesurfactant in this process can be, but is not limited to being, made upof derivatives of sulfonates, sulfates, carboxylates, phosphates,ammoniums, quaternary ammoniums, betaines, sulfobetaines, imides,anhydrides, polyoxyethylene (eg. PEO/PEG/PPG), polyols (eg. sucrose,sorbitan, glycerol etc), polypeptides and polyglycidyls. The hydrophobictail of the surfactant in this process can be, but is not limited tobeing, made up of straight and branched chain alkyls, olefins andpolyolefins, rosin derivatives, PPO, hydroxyl and polyhydroxystearicacid type chains, perfluoroalkyls, aryls and mixed alkyl-aryls,silicones, lignin derivatives, and partially unsaturated versions ofthose mentioned above. Surfactants for this process can also becatanionic, bolaforms, gemini, polymeric and polymerisable typesurfactants. Preferably, polyisobutylene succinimides may be used.

Examples of preferred surfactants are the Span, Brij and Tween range(Sigma-Aldrich), the Solsperse, Ircosperse and Colorburst range(Lubrizol), the OLOA range (Chevron Chemicals) and Aerosol-OT (A-OT)(Aldrich). A-OT (dioctyl sulfosuccinate sodium salt), Span 80 and Span85 (partially unsaturated sorbitan trioleate), Solsperse 17000, and OLOA11000 are particularly useful to disperse and coat titania in thisreaction. Single surfactants as well as blends of surfactants may beused.

Preferably the polymerisation according to the invention is a freeradical polymerisation.

Typical process conditions are described for titanium dioxide particlescoated according to the invention. Titanium dioxide is added to anon-polar hydrocarbon solvents, preferably dodecane andPDMS-methacrylate.

Preferably, a surfactant is added. Preferably polyisobutylenesuccinimides or a sorbitan mono-, di- or tri-oleate such as Span 85 maybe used. Examples of preferred surfactants are the Span, Brij and Tweenrange (Sigma-Aldrich), the Solsperse, Ircosperse and Colorburst range(Lubrizol), the OLOA range (Chevron Chemicals) and Aerosol-OT (A-OT)(Aldrich). A-OT (dioctyl sulfosuccinate sodium salt), Span 80 and Span85 (partially unsaturated sorbitan trioleate), Solsperse 17000, and OLOA11000 are particularly useful to disperse and coat titania in thisreaction. Single surfactants as well as blends of surfactants may beused. The solution is stirred or lightly sonicated or milled or highshear mixed to disperse the pigment. A comonomer, preferably MMA, apolymerisable dye, preferably a dye of Table 1, and optionally a chaintransfer agent, preferably octanethiol are then added to the solutionwhich is stirred under nitrogen, then heated to 60-90° C., preferably85° C., optionally in a sonic bath. Sonication is optionally applied tothe reaction and an initiator, preferably azobisisobutyronitrile isadded to initiate polymerisation. Depending on the surfactant used, thereaction mixture needs solely stirring. The reaction is allowed toproceed for 2-6, preferably 4 hours after which time the reaction iscooled and the particles are cleaned by centrifugation and redispersionin dodecane if required.

Polymer particles prepared according to the invention are preferablyspherical particles with a size (diameter) in the range of 50-1200 nm,preferably 400-1000 nm, especially 400-700 nm, and preferably with amonodisperse size distribution. Smaller or larger particles can befurther separated if required by centrifugation. Particle sizes aredetermined by photon correlation spectroscopy of hydrocarbon particledispersions by a common apparatus such as a Malvern NanoZS particleanalyser or preferably by SEM (Scanning Electron Microscopy) and imageanalysis.

Particles of the invention are primarily designed for use inelectrophoretic displays, especially for use in mono, bi or polychromalelectrophoretic devices. A typical electrophoretic display preferablyconsists of the particles dispersed in a low polar or non-polar solventalong with additives to improve electrophoretic properties, such asstability and charge. Examples of such dispersions are well described inthe literature, for example U.S. Pat. No. 7,247,379; WO 99/10767; US2007/0128352; U.S. Pat. No. 7,236,290; U.S. Pat. No. 7,170,670; U.S.Pat. No. 7,038,655; U.S. Pat. No. 7,277,218; U.S. Pat. No. 7,226,550;U.S. Pat. No. 7,110,162; U.S. Pat. No. 6,956,690; U.S. Pat. No.7,052,766; U.S. Pat. No. 6,194,488; U.S. Pat. No. 5,783,614; U.S. Pat.No. 5,403,518; U.S. Pat. No. 5,380,362.

Typical additives to improve the stability of the fluid (either bysteric stabilisation or by use as a charging agent) are known to expertsin the field and include (but are not limited to) the Brij, Span andTween series of surfactants (Aldrich), the Solsperse, Ircosperse andColorburst series (Lubrizol), the OLOA charging agents (ChevronChemicals) and Aerosol-OT (Aldrich).). Preferable surfactant additivesin this work are Solsperse range and A-OT, and even more preferablySolsperse 17,000, 13650, 11000 and Solplus K500, A-OT and Span 85.Typical surfactants used in this process are cationic, anionic,zwitterionic or non-ionic with a hydrophilic portion usually termed thehead group which is mono-, di- or polysubstituted with a hydrophobicportion usually termed the tail. The hydrophilic head group of thesurfactant in this process can be, but is not limited to being, made upof derivatives of sulfonates, sulfates, carboxylates, phosphates,ammoniums, quaternary ammoniums, betaines, sulfobetaines, imides,anhydrides, polyoxyethylene (e.g. PEO/PEG/PPG), polyols (e.g. sucrose,sorbitan, glycerol etc), polypeptides and polyglycidyls. The hydrophobictail of the surfactant in this process can be, but is not limited tobeing, made up of straight and branched chain alkyls, olefins andpolyolefins, rosin derivatives, PPO, hydroxyl and polyhydroxystearicacid type chains, perfluoroalkyls, aryls and mixed alkyl-aryls,silicones, lignin derivatives, and partially unsaturated versions ofthose mentioned above. Surfactants for this process can also becatanionic, bolaforms, gemini, polymeric and polymerisable typesurfactants.

Any other additives to improve the electrophoretic properties can beincorporated provided they are soluble in the formulation medium, inparticular thickening agents or polymer additives designed to minimisesettling effects.

The dispersion solvent can be chosen primarily on the basis ofdielectric constant, refractive index, density and viscosity. Apreferred solvent choice would display a low dielectric constant (<10,more preferably <5), high volume resistivity (about 10¹⁵ ohm-cm), a lowviscosity (less than 5 cst), low water solubility, a high boiling point(>80° C.) and a refractive index and density similar to that of theparticles. Tweaking these variables can be useful in order to change thebehavior of the final application. For example, in a slow-switchingapplication such as poster displays or shelf labels, it can beadvantageous to have an increased viscosity to improve the lifetime ofthe image, at the cost of slower switching speeds. However in anapplication requiring fast switching, for example e-books and displays,a lower viscosity will enable faster switching, at the cost of thelifetime in which the image remains stable (and hence an increase inpower consumption as the display will need more frequent addressing).The preferred solvents are often non-polar hydrocarbon solvents such asthe Isopar series (Exxon-Mobil), Norpar, Shell-Sol (Shell), Sol-Trol(Shell), naphtha, and other petroleum solvents, as well as long chainalkanes such as dodecane, tetradecane, decane and nonane). These tend tobe low dielectric, low viscosity, and low density solvents. A densitymatched particle/solvent mixture will yield much improvedsettling/sedimentation characteristics and thus is desirable. For thisreason, often it can be useful to add a halogenated solvent to enabledensity matching. Typical examples of such solvents are the Halocarbonoil series (Halocarbon products), or tetrachlorethylene, carbontetrachloride, 1,2,4-trichlorobenzene and similar solvents. The negativeaspect of many of these solvents is toxicity and environmentalfriendliness, and so in some cases it can also be beneficial to addadditives to enhance stability to sedimentation rather than using suchsolvents.

The preferred additives and solvents used in the formulation of theparticles of the invention are OLOA11000 (Chevron Chemicals), Ircosperse2153 (Lubrizol Ltd), and dodecane (Sigma Aldrich).

Usually electrophoretic fluids comprise a charged inorganic nanoparticlesuch as titania, alumina or barium sulphate, coated with a surface layerto promote good dispersibility in dielectric media and a dielectricfluid media. The solvents and additives used to disperse the particlesare not limited to those used within the examples of this invention andmany other solvents and/or dispersants can be used. Lists of suitablesolvents and dispersants for electrophoretic displays can be found inexisting literature, in particular WO 99/10767) and WO 2005/017046) TheElectrophoretic fluid is then incorporated into an Electrophoreticdisplay element by a variety of pixel architectures, such as can befound in C. M. Lampert, Displays; 2004, 25(5) published by Elsevier B.V., Amsterdam.

Electrophoretic displays comprise typically, the electrophoretic displaymedia in close combination with a monolithic or patterned backplaneelectrode structure, suitable for switching the pixels or patternedelements between the black and white optical states or theirintermediate greyscale states.

The electrophoretic particles according to the present invention aresuitable for all known electrophoretic media and electrophoreticdisplays, e.g. flexible displays, TIR-EPD (total internal reflectionelectrophoretic devices), one particle systems, two particle systems,dyed fluids, systems comprising microcapsules, microcup systems, air gapsystems and others as described in C. M. Lampert, Displays; 2004, 25(5)published by Elsevier B. V., Amsterdam. Examples of flexible displaysare dynamic keypads, e-paper watches, dynamic pricing and advertising,e-readers, rollable displays, smart card media, product packaging,mobile phones, lab tops, display card, digital signage.

Particles of the invention may also be used in optical, electrooptical,electronic, electrochemical, electrophotographic, electrowettingdisplays and/or devices, e.g. TIR (total internal reflection electronicdevices), and in security, cosmetic, decorative, and diagnosticapplications. The use in electrowetting displays is preferred.Electrowetting (ew) is a physical process where the wetting propertiesof a liquid droplet are modified by the presence of an electric field.This effect can be used to manipulate the position of a coloured fluidwithin a pixel. For example, a nonpolar (hydrophobic) solvent containingcolourant can be mixed with a clear colourless polar solvent(hydrophilic), and when the resultant biphasic mixture is placed on asuitable electrowetting surface, for example a highly hydrophobicdielectric layer, an optical effect can be achieved. When the sample isat rest, the coloured non-polar phase will wet the hydrophobic surface,and spread across the pixel. To the observer, the pixel would appearcoloured. When a voltage is applied, the hydrophobicity of the surfacealters, and the surface interactions between the polar phase and thedielectric layer are no longer unfavourable. The polar phase wets thesurface, and the coloured non-polar phase is thus driven to a contractedstate, for example in one corner of the pixel. To the observer, thepixel would now appear transparent. A typical electrowetting displaydevice consists of the particles in a low polar or non-polar solventalong with additives to improve properties, such as stability andcharge. Examples of such electrowetting fluids are described in theliterature, for example in WO2011/017446, WO 2010/104606, andWO2011075720.

The disclosures in the cited references are thus expressly also part ofthe disclosure content of the present application. In the claims and thedescription, the words “comprise/comprises/comprising” and“contain/contains/containing” mean that the listed components areincluded but that other components are not excluded. The followingexamples explain the present invention in greater detail withoutrestricting the scope of protection.

EXAMPLES

Reagents are purchased from Sigma-Aldrich unless otherwise stated. PDMSmonomer is purchased from Gelest Inc. Titanium Dioxide used is R960,obtained from DuPont. Magenta and Yellow dyes used to make particles arepreviously reported in WO 2012/019704.

Particle size is measured by SEM.

The characterisation of the formulations is performed using a MalvernNanoZS particle analyser. This instrument measures the size of particlesin dispersion and the zeta potential of an electrophoretic fluid. TheZeta potential (ZP) is derived from the real-time measurement of theelectrophoretic mobility and thus is an indicator of the suitability ofthe fluid for use in electrophoretic applications.

Electrophoretic mobility measurements are made on a Malvern ZetasizerNano ZS. The measurement is made using a combination of Laser Dopplervelocimetry and phase analysis light scattering. The formulations arefirst diluted (1 drop of dispersion into approximately 2 ml dodecane).The measurement is made using the Universal Dip cell (suitable fornon-aqueous systems) and a glass cuvette. Mobility unit of measure isμmcm/Vs.

Reflectivity Measurements

Reflectivity measurements are made using an X-rite Color i5 benchtopspectrophotometer. All measurements are made in glass cells with a 50micron cell depth. The cells have no polyimide coating and no ITOelectrodes. The cells are capillary filled and measurements are madeimmediately after filling. The cell is measured in the X-ritespectrophotometer. The reflectivity measurements are made with a blackbackground, the values obtained are L*, a*, b*, X, Y, Z, x and y. The L*component represents the lightness of the sample (L*=0 being a blacksample and L*=100 a white sample). The a* value represents theco-ordinate where the sample lies between red and green (negative valuesindicating a green sample and positive a red sample). The b* componentrepresents the co-ordinate where the sample lies between yellow and blue(here negative values indicate a blue sample and positive a yellowsample). The Y value is derived from the CIE xyY colour space, where Yis defined to be the brightness or luminance of the sample, and alsoscales between 0-100.

Example 1(E)-4,4′-(4-((2,6-dicyano-4-nitrophenyl)diazenyl)-2-methoxy-5-(3,5,5-trimethylhexanamido)phenylazanediyl)bis(butane-4,1-diyl)diacrylate(Dye 3)

Step 1:4,4″-(5-acetamido-2-methoxyphenylazanediyl)bis(butane-4,1-diyl)diacetate

A stirred mixture of 3′-amino-4′-methoxyacetanilide (18.0 g, 0.1 mol),4-bromobutyl acetate (48.8 g, 0.25 mol), 1-methyl-2-pyrrolidinone (50ml) and sodium bicarbonate (55.2 g, 0.66 mol) is heated in an oil bathat 105° C. overnight, allowed to cool and then poured into water (500ml), After stirring for 30 minutes, the oil that separates is extractedwith dichloromethane (150 ml), the organic layer is dried (MgSO₄) andevaporated to give a thick brown oil (57.0 g). The oil is used directlywithout further purification (95% purity).

Step 2: 4,4′-(5-amino-2-methoxyphenylazanediyl)dibutan-1-ol

Crude4,4′-(5-acetamido-2-methoxyphenylazanediyl)bis(butane-4,1-diyl)diacetate(0.1 mol) is dissolved in dioxane (200 ml) and 1M LiOH (300 ml) isadded. After 15 minutes, the reaction is neutralised with 35% HCl (5 ml)then evaporated to give a brown oil. The oil is dissolved in a mixtureof water (200 ml) and 35% HCl (100 ml) and heated for 4 h at 90° C.,allowed to cool to RT, basified to pH 11.0 and the resultant oil isextracted with DCM (2×150 ml), dried (MgSO₄) and evaporated to give adark brown viscous oil. (28.3 g, 100%). The crude product is useddirectly without purification.

Step 3:N-(3-(Bis(4-hydroxybutyl)amino)-4-methoxyphenyl)-3,5,5-trimethylhexanamide

4,4′-(5-Amino-2-methoxyphenylazanediyl)dibutan-1-ol (50 mmol) isdissolved in dichloromethane (200 ml) and to this is added triethylamine(7.6 g, 75 mmol). 3,5,5-Trimethylhexanoyl chloride (8 ml) is addeddropwise. Methanol (100 ml) is added and the reaction is stirredovernight and is used directly without further purification.

Step 4:(E)-N-(5-(Bis(4-hydroxybutyl)amino)-2-((2-bromo-6-cyano-4-nitrophenyl)diazenyl)-4-methoxyphenyl)-3,5,5-trimethylhexanamide

Sulfuric acid (80% w/w, 75 ml) is cooled to 5° C. and6-bromo-2-cyano-4-nitroaniline (9.7 g, 40 mmol) is added and stirred for10 minutes at <5° C. until fully dispersed. Nitrosyl sulfuric acid 40%(w/w) in sulfuric acid (15.3 g, 0.048 mol) is added in portions at 3-5°C. over 30 minutes, then stirred for a further hour at <5° C.N-(3-(Bis(4-hydroxybutyl)amino)-4-methoxyphenyl)-3,5,5-trimethylhexanamide(assume 41 mmol) is diluted with methanol (100 ml), cooled externally inan ice bath to 5° C. and solid ice (50 g) and water (50 ml) are added.Sulfamic acid (10 ml) is added. The above diazonium salt solution isadded dropwise over 1 hour. The reaction is stirred overnight, then thesolid filtered-off and dried overnight at 40° C. (13.4 g, 50%). Thecrude product is recrystallised from hot IMS to give the required dye asa green crystalline solid (8.9 g, 32%).

Step 5:(E)-N-(5-(bis(4-hydroxybutyl)amino)-2-((2,6-dicyano-4-nitrophenyl)diazenyl)-4-methoxyphenyl)-3,5,5-trimethylhexanamide

N-(5-(Bis(4-hydroxybutyl)amino)-2-((2-bromo-6-cyano-4-nitrophenyl)diazenyl)-4-methoxyphenyl)-3,5,5-trimethylhexanamide(8.8 g, 13.0 mmol) is suspended in 1-methyl-2-pyrrolidinone (15 ml) andwarmed to 55° C. to dissolve. Zinc cyanide (0.82 g, 7 mmol) followed bycopper(I) cyanide (0.4 mg, 0.45 mmol) are added and the reaction heatedto 105° C. (bath temp). After 3 h, external heating is removed andmethanol (45 ml) is added. The resultant crystalline solid is filteredoff. The solid is recrystallised from IMS (6.1 g, 75%).

Step 6:(E)-4,4′-(4-((2,6-dicyano-4-nitrophenyl)diazenyl)-2-methoxy-5-(3,5,5-trimethylhexanamido)phenylazanediyl)bis(butane-4,1-diyl)bis(3-chloropropanoate)

(E)-N-(5-(Bis(4-hydroxybutyl)amino)-2-((2,6-dicyano-4-nitrophenyl)diazenyl)-4-methoxyphenyl)-3,5,5-trimethylhexanamide(6.0 g, 9.7 mmol) and sodium bicarbonate (8.1 g, 97 mol) are suspendedin dichloromethane (120 ml) and 3-chloropropionyl chloride (3.7 g, 29.1mmol) added. The mixture is heated at 40° C. overnight. Methanol (300ml) is added and the mixture is concentrated in vacuo to half volume.The precipitated tarry solid is filtered off. The solid is added todichloromethane (100 ml) and stirred for 5 minutes to dissolve, beforeinorganics are removed by filtration. The dichloromethane solution isevaporated to give the crude product as a black tarry solid (7.7 g,90%). The material was purified over silica gel, eluting with 2-5% ethylacetate in dichloromethane. Combination and evaporation of the purefractions afford the required compound as a black tarry solid (6.8 g,80%), which is >99% pure by HPLC.

Step 7:(E)-4,4′-(4-((2,6-dicyano-4-nitrophenyl)diazenyl)-2-methoxy-5-(3,5,5-trimethylhexanamido)phenylazanediyl)bis(butane-4,1-diyl)bis(acrylate)

(E)-4,4″-(4-((2,6-dicyano-4-nitrophenyl)diazenyl)-2-methoxy-5-(3,5,5-trimethylhexanamido)phenyl-azanediyl)bis(butane-4,1-diyl)bis(3-chloropropanoate)(6.8 g, 8.5 mmol) is dissolved in dichloromethane (68 ml) andtriethylamine (6.0 ml, 43 mmol) is added. The reaction is warmed for 3 hat 35° C. The solution is washed with 0.2 N HCl, then with water, dried(Na₂SO₄) and filtered. The solution is evaporated and the resultanttarry solid redissolved in dichloromethane (200 ml), diluted withmethanol (400 ml) and stirred overnight allowing solvent to slowlyevaporate. The resultant solid is filtered-off, washed with methanol onthe filter and dried under high vacuum until a constant weight wasobtained. The required dye was obtained as a dark blue solid (5.4 g,87%). Mp: 120-121° C., λ_(max) (EtOAc) 642 nm (98,000), ½ band width=70nm. ¹H NMR (CDCl₃, 300 MHz) δ 0.92 (9H, 5), 1.03 (3H, d, J 6.6), 1.17(1H, dd, J 14.0, J 6.6), 1.34 (1H, dd, J 14.0, J 3.7), 1.81 (8H, m),2.16 (1H, m), 2.42 (1H, dd, J 14.0, J 8.0) 2.52 (1H, dd, J 14.0, J 6.5),3.71 (4H, m), 3.88 (3H, s), 4.23 (4H, t, J 6.0), 5.84 (2H, dd, J 10.5, J1.5), 6.13 (2H, dd, J 17.3, J 10.5), 6.42 (2H, J 17.3, J 1.5), 7.54 (1H,s), 8.32 (1H, s), 8.63 (2H, s), 9.27 (1H, br. s),

Example 2 Preparation of a Dispersion of Reflective Particles Example 2aPreparation of a Dispersion of Reflective Particles Comprising Dye 2

Polydimethylsiloxane monomethacrylate terminated, mw. 10,000 (2.08 g),dodecane (100 ml), titanium dioxide (4.12 g) and Span 80 (0.6 g) arecharged to a 250 ml 3-neck round bottom flask. The flask is placed in anultrasonic bath and is subjected to low power ultrasound for 30 minutes.In a separate flask, methyl methacrylate (11.0 ml), Dye 2 (0.25 g), AIBN(107 mg) and octane thiol (126 μl) are mixed. The contents of the secondflask are added to the first, and the 3-neck flask is immersed in asonic bath at 80° C., and the contents are stirred with an overheadstirrer at 300 rpm, under a flow of nitrogen. After 4 hours, the flaskis allowed to cool to room temperature and the contents are filteredthough a 50 micron cloth. The magenta dispersion is cleaned bycentrifugation and replacing the supernatant with clean dodecane.Average particle size is 520 nm.

Examples 2b-2h

Further reflective particles are similarly prepared, formulated andmeasured (see Table 2).

TABLE 2 Example Dye Dye TiO2 Size Mobility No. No. (g) Colour (g) (nm)L* a* b* Y (3 wt % Span 85) 2a Dye 2 0.25 Magenta 4.12 520 2b Dye 20.259 Magenta 4.12 823 23.78 8.37 −2.58 4.03 0.2065 2c N/A 0 White 4.12660 40.43 −1.37 −1.08 11.51 0.1239 2d Dye 2 0.259 Magenta 0.00 725 18.8512.26 −4.9 2.71 0.1447 2e Dye 2 0.103 Magenta 4.14 670 30.7 12.55 −5.186.53 0.1789 2f Dye 3 0.103 Cyan 4.14 704 32.29 −7.2 −6.73 7.22 2g Dye 20.026 Magenta 4.14 749 2h Dye 1 0.103 Yellow 4.14

Example 3 Electrophoretic Formulations Containing Dispersions ofParticles of Example 2

Ink formulations (2.00 g) are made and are composed of 3 wt % ofparticles of Example 2 and 3 wt % of surfactant. The surfactants usedare either Span 85 or AOT. This is indicated in Table 2. The 2.00 gformulations are vortex mixed and then roller mixed for 30 minutes.

Reflectivity and electrophoretic mobility measurements are then made.Results are summarised in Table 2.

Particles containing both dyes and white pigments show an improvedreflectivity over coloured particles containing no white pigment.

There is no colour shift towards other hues, only towards white, so thefluids appear brighter.

Example 4 Preparation of Reflective Particles incorporating Dye 1

Polydimethylsiloxane monomethacrylate terminated, mw. 10,000 (Gelest,2.08 g), dodecane (75 g), titanium dioxide (10.30 g), and Span 85 (0.515g) are charged to a 250 ml 3-neck round bottom flask. The flask isfitted with an overhead stirrer, condenser and nitrogen bubbler. Theflask is subjected to 37 Hz power ultrasound for 30 minutes.

In a separate flask, methyl methacrylate (10.3 g), AIBN (0.214 g), Dye 1(0.103 g), and octane thiol (0.126 ml) are combined. The flask with TiO2is placed in the sonic bath at 80° C., and the contents are stirred withan overhead stirrer at 300 rpm, under a flow of nitrogen. The monomersolution is then added to this dispersion at a rate of 3.8 mL/hour.After 4 hours, the flask is allowed to cool to room temperature and thecontents are filtered though a 50 micron cloth. The dispersion iscleaned by centrifugation at 10 000 rpm for 20 minutes each, replacingthe supernatant with dodecane five times.

Further reflective particles are similarly prepared, formulated andmeasured. Average particle size for these reactions is ˜500 nm. Detailsare shown in Table 3.

TABLE 3 Example No. Dye No. Dye (g) Colour TiO2 (g) L* a* b* Y 4a 10.2059 Y 10.3 77.83 −12.60 34.46 52.924 4b 1 0.3090 Y 10.3 76.62 −13.6540.02 50.900 4c 1 0.4120 Y 10.3 76.79 −14.31 45.77 51.180 4d 1 0.5150 Y10.3 77.46 −14.92 49.08 52.294 4e 3 5.3090 C 10.3 55.79 −16.71 −22.3523.700 4f 2 0.3090 M 10.3 50.95 38.47 −9.92 19.225

Example 5 Preparation of Reflective Particles Incorporating Dye 1, UsingMethacrylic Acid

Polydimethylsiloxane monomethacrylate terminated, mw. 10,000 (Gelest,2.08 g), dodecane (53.1 g), titanium dioxide (10.30 g), and Span 85(0.515 g) are charged to a 250 ml 3-neck round bottom flask. The flaskis fitted with an overhead stirrer, condenser and nitrogen bubbler. Theflask is subjected to ultrasound (37 Hz) for 30 minutes.

In a separate flask, methacrylic acid (10.3 g), dye 1 (0.515 g), toluene(19.1 g) and octane thiol (0.126 ml) are combined and taken up in asyringe.

In a separate flask, AIBN (0.214 g) is dissolved in toluene (7.5 g) andthe resulting solution taken up in a syringe.

The first flask is placed in the sonic bath at 80° C., and the contentsare stirred with an overhead stirrer at 300 rpm, under a flow ofnitrogen. The monomer solution is then added to this dispersion using asyringe pump.

The initiator solution is added at the same time using a second syringepump.

On completion, the flask is allowed to cool to room temperature and thecontents are filtered though a 50 micron cloth. The dispersion iscleaned by centrifugation. Centrifugations are carried out at 10 000 rpmfor 20 minutes each, replacing the supernatant with dodecane; this isrepeated five times.

These particles are formulated and measured. Results are shown in Table4.

TABLE 4 L* a* b* Y 75.69 −14.00 52.38 49.379

1-19. (canceled)
 20. Particles comprising pigment core particlesencapsulated by a polymer comprising monomer units of at least onepolymerisable dye, at least one co-monomer, at least one polymerisablesteric stabiliser, optionally at least one charged co-monomer, andoptionally at least one crosslinking co-monomer.
 21. The particlesaccording to claim 20, wherein a single pigment core particle isencapsulated by the polymer and wherein the particles comprise at leastone surfactant.
 22. The particles according to claim 20, wherein asingle pigment core particle is coated with at least one surfactant andencapsulated by a polymer.
 23. The particles according to claim 21,wherein the least one surfactant is soluble in non-polar organicsolvents.
 24. The particles according to claim 20, wherein the pigmentcore particle is titanium dioxide in the rutile, anatase, or amorphousmodification.
 25. The particles according to claim 20, wherein the atleast one polymerisable dye is selected from the group consisting of azodyes, metallised dyes, anthraquinone dyes, phthalocyanine dyes,benzodifuranones dyes, Brilliant Blue derivatives, pyrroline dyes,squarilium dyes, triphendioxazine dyes, and mixtures of these dyes. 26.The particles according to claim 20, wherein the at least onepolymerisable dye is at least one dye of Formula (VII)

wherein X₁, X₂, and X₃ are independently of one another H or anelectron-withdrawing group; R₁ is H or OR′ with R′=a linear, branched orcyclic alkyl group; R₂ is a linear, branched or cyclic alkyl group; R₃and R₄ are independently of one another groups of the structure L₃-Y₃,L₃, and L₄ are linker groups and independently of one another linear orbranched, substituted or unsubstituted alkylene groups where one or morenon-adjacent carbon atoms may be replaced by O, S and/or N, preferablyO; Y₃, and Y₄ are independently of one another polymerisable groups;wherein at least one of R₃ and R₄ comprises a polymerisable group and atleast one of X₁, X₂, and X₃ is an electron-withdrawing group.
 27. Theparticles according to claim 20, wherein the polymerisable stericstabiliser is a poly(dimethylsiloxane) macromonomer with at least onepolymerisable group and a molecular weight in the range of 1000-50000.28. The particles according to claim 20, wherein the polymerisablesteric stabiliser is a methacryloyloxypropyl terminatedpolydimethylsiloxanes.
 29. The particles according to claim 20, whereinthe percentage of polymerisable steric stabiliser is at least 5% byweight based on the weight of the polymer particle.
 30. The particlespolymer particles according to claim 20, wherein the particles arecoloured and wherein the polymer particles have a diameter of 400-1000nm.
 31. A process for the preparation of particles according to claim 20comprising a) dispersing at least one pigment particle in a solution ofat least one polymerisable steric stabiliser in a non-polar organicsolvent, preferably an aliphatic hydrocarbon; b) adding at least onepolymerisable dye, at least one co-monomer, at least one initiator, andoptionally at least one chain transfer agent; c) subjecting thedispersion of step b) to heating and optional sonication, milling,stirring or high shear mixing for polymerisation, d) optionally washingby repeated centrifugation or stirred filtration and redispersion infresh solvent, and e) optionally isolating the resulting coatedparticles.
 32. The process according to claim 31, wherein at least onesurfactant is used in step a).
 33. A method comprising utilizing theparticles according to claim 20 in optical, electrooptical, electronic,electrochemical, electrophotographic, electrowetting and electrophoreticdisplays and/or devices, and in security, cosmetic, decorative, anddiagnostic applications, preferably in mono, bi or polychromalelectrophoretic devices.
 34. An electrophoretic fluid comprisingparticles according to claim
 20. 35. An electrophoretic fluid comprisingparticles prepared by the process of claim
 31. 36. An electrophoreticdisplay device comprising an electrophoretic fluid according to claim34.
 37. An electrophoretic display device comprising an electrophoreticfluid according to claim
 35. 38. The electrophoretic display deviceaccording to claim 37, wherein the electrophoretic fluid is applied by atechnique selected from inkjet printing, slot die spraying, nozzlespraying, and flexographic printing, or any other contact or contactlessprinting or deposition technique.